River fishing:
A lot of good places are not accessible or very hard to access without a boat and if it is accessible, it is matter of time to become public knowledge and then guides avoid it.

Ocean fishing:
I used my GPS for fishing Marlins in Mexico and a week later with a new guide with bigger and safer boat (this is another good srory) when things were slow, I told the captain let's try this spot and believe it or not I caught 3 in that general area. I have heard that westport charters don't let you use them. But ocean fishing is different.